1. Field of the Invention
This application relates to optical devices that transform light between linearly and elliptically polarized states.
2. Description of Related Art
Devices that transform linearly polarized light to circularly polarized light and the reverse are known in the literature. To make such optical devices, one may use one birefringent fiber with two beams of light of equal frequency and amplitude (or, equivalently, one beam that is the vector sum of these two beams). If the two beams are propagated perpendicular to the optic axis, circularly polarized light may result. Alternatively, linearly polarized light may be transformed to circularly polarized light by using one beam and two fibers.
In practice, constructing a single-beam transformer of linearly to circularly polarized light involves first starting with a length of transforming fiber greater than a predetermined length, and performing several iterations of cutting and measuring polarization until the polarization is deemed to be circular to within some specification. Needless to say, this is a tedious and lengthy procedure requiring lots of guesswork.
A method of fabricating a transformer of polarized light is presented herein, which can comprise twisting a birefringent fiber, having two ends, about its central axis through an angle approximately equal to an odd multiple of xcfx80/4 radians, at a distance of slightly more than a preselected multiple of a beatlength from a first end of the fiber, shining light substantially of a preselected first state of polarization through a preselected end of the fiber and fine tuning the polarization of the light exiting an end of the fiber opposite the preselected end by heating the fiber between the twist and the first end, so as to cause the core to diffuse into the cladding, until the exiting light can be substantially of a preselected second state of polarization. The birefringent fiber may be twisted while being, or after having been, heated near the location of the twist. The preselected first state of polarization may be linear, the preselected end of the fiber can be the second end, and the preselected second state of polarization may be elliptical with a preselected eccentricity or circular. Alternatively, the preselected first state of polarization may be elliptical with a preselected eccentricity or circular, the preselected end of the fiber can be the first end, and the preselected second state of polarization may be linear. The preselected multiple of a beatlength may be xc2xc. In one embodiment, the fiber may be twisted into a corkscrew shape.
A method of transforming substantially linearly polarized light into substantially elliptically polarized light may also be presented, which may comprise twisting a birefringent fiber, having two ends, through an angle approximately equal to an odd multiple of xcfx80/4 radians, at a distance of slightly more than a preselected multiple of a beatlength from a first end of the fiber, shining substantially linearly polarized light through a second end of the fiber and fine tuning the polarization of the light exiting the first end of the fiber by heating the fiber between the twist and the first end, so as to cause the core to diffuse into the cladding, until the exiting light can be substantially elliptically polarized with a preselected eccentricity. The elliptically polarized light may be circularly polarized. The preselected multiple of a beatlength may be an odd multiple of one quarter. The birefringent fiber may be twisted while being, or after having been heated near the location of the twist. In one embodiment, the fiber may be twisted into a corkscrew shape.
A method of transforming substantially elliptically polarized light into substantially linearly polarized light may also be presented, which can comprise twisting a birefringent fiber, having two ends, about its central axis through an angle approximately equal to an odd multiple of xcfx80/4 radians, at a distance of slightly more than a preselected multiple of a beatlength from a first end of the fiber, shining substantially elliptically polarized light with a preselected eccentricity through a first end of the fiber and fine tuning the polarization of the light exiting the second end of the fiber by heating the fiber between the twist and the first end, so as to cause the core to diffuse into the cladding, until the exiting light is substantially linearly polarized. The elliptically polarized light may be circularly polarized. The preselected multiple of a beatlength may be an odd multiple of one quarter. The birefringent fiber may be twisted while being, or after having been heated near the location of the twist. In one embodiment, the fiber may be twisted into a corkscrew shape.
A method of fabricating a transformer of polarized light may also be presented, which can comprise splicing a first end of a first birefringent fiber, having a central axis and two ends, to a second end of a second birefringent fiber, having a central axis and two ends, and having a length of slightly more than a preselected multiple of a beatlength, where the central axis of the second birefringent fiber can be rotated through an angle approximately equal to an odd multiple of xcfx80/4 radians with respect to the central axis of the first birefringent fiber, shining substantially linearly polarized light through the second end of the first fiber and fine tuning the polarization of the light exiting the first end of the second fiber by heating the second fiber, so as to cause the core to diffuse into the cladding, until the exiting light is substantially elliptically polarized with a preselected eccentricity. The preselected multiple of a beatlength may be an odd multiple of one quarter.
A method of fabricating a transformer of polarized light may also be presented, which may comprise splicing a first end of a first birefringent fiber, having a central axis and two ends, to a second end of a second birefringent fiber, having a central axis and two ends, and having a length of slightly more than a preselected multiple of a beatlength, where the central axis of the second birefringent fiber is rotated through an angle approximately equal to an odd multiple of xcfx80/4 radians with respect to the central axis of the first birefringent fiber, shining substantially elliptically polarized light through the first end of the second fiber and fine tuning the polarization of the light exiting the second end of the first fiber by heating the second fiber, so as to cause the core to diffuse into the cladding, until the exiting light is substantially linearly polarized. The preselected multiple of a beatlength may be an odd multiple of one quarter.
A method of transforming substantially linearly polarized light into substantially elliptically polarized light may also be presented, which can comprise splicing a first end of a first birefringent fiber, having a central axis and two ends, to a second end of a second birefringent fiber, having a central axis and two ends, and having a length of slightly more than a specified multiple of a beatlength, where the central axis of the second birefringent fiber is rotated through an angle approximately equal to an odd multiple of xcfx80/4 radians with respect to the central axis of the first birefringent fiber, shining substantially linearly polarized light through the second end of the first fiber and fine tuning the polarization of the light exiting the first end of the second fiber by heating the second fiber, so as to cause the core to diffuse into the cladding, until the exiting light is substantially elliptically polarized with a preselected eccentricity. The specified multiple of a beatlength may be an odd multiple of one quarter.
A method of transforming substantially elliptically polarized light into substantially linearly polarized light may also be presented, which can comprise splicing a first end of a first birefringent fiber, having a central axis and two ends, to a second end of a second birefringent fiber, having a central axis and two ends, and having a length of slightly more than a specified multiple of a beatlength, where the central axis of the second birefringent fiber is rotated through an angle approximately equal to an odd multiple of xcfx80/4 radians with respect to the central axis of the first birefringent fiber, shining substantially elliptically polarized light with a preselected eccentricity through the first end of the second fiber and fine tuning the polarization of the light exiting the second end of the first fiber by heating the second fiber, so as to cause the core to diffuse into the cladding, until the exiting light is substantially linearly polarized. The specified multiple of a beatlength may be an odd multiple of one quarter.
A transformer of light between substantially elliptical and substantially linear polarization states may be presented, which can comprise a birefringent fiber, having two ends, twisted about its central axis through an angle approximately equal to an odd multiple of xcfx80/4 radians, at a distance of slightly more than a preselected multiple of a beatlength from a first end of the fiber, wherein the fiber can contain a core which runs lengthwise through the fiber surrounded by a cladding and a portion of the core between the twist and a first end of the fiber can have diffused into a portion of the cladding surrounding it. The preselected multiple of a beatlength can be an odd multiple of one quarter. The portion of the core may diffuse into the portion of the cladding surrounding it by the application of heat to the portion of the fiber between the first end and the twist, which heat can be applied until substantially linearly polarized light entering a second end of the fiber can exit the first end substantially elliptically polarized with a preselected eccentricity, or, alternatively, until substantially elliptically polarized light with a preselected eccentricity entering a first end of the fiber can exit the second end substantially linearly polarized. The twist in the birefringent fiber may be formed by twisting the fiber while it may be being heated, or after it can have been heated near the location of the twist. The fiber may be twisted into a corkscrew shape.
A transformer of light between substantially linear and substantially elliptical polarization states may also be presented, which can comprise a first birefringent fiber, having a central axis and two ends, containing a core which runs lengthwise through the fiber surrounded by a cladding and a second birefringent fiber, having a central axis and two ends, containing a core which runs lengthwise through the fiber surrounded by a cladding, and having a length of slightly more than a preselected multiple of a beatlength, where the central axis of the second birefringent fiber may be rotated through an angle approximately equal to an odd multiple of xcfx80/4 radians with respect to the central axis of the first birefringent fiber, and the first end of the second birefringent fiber may be spliced to the second end of the first birefringent fiber, and where a portion of the core in the second fiber can have diffused into a portion of the cladding surrounding it. The preselected multiple of a beatlength may be an odd multiple of one quarter. The portion of the core may diffuse into the portion of the cladding surrounding it by the application of heat to the second fiber, which heat can be applied until substantially linearly polarized light entering a second end of the first fiber can exit the first end of the second fiber substantially elliptically polarized with a preselected eccentricity, or alternately, until substantially elliptically polarized light with a preselected eccentricity entering a first end of the second fiber can exit the second end of the first fiber substantially linearly polarized.